Parapsychology is the study of paranormal psychic phenomena, including ESP. Parapsychology has been criticized for continuing investigation despite being unable to provide convincing evidence for the existence of any psychic phenomena after more than a century of research.[2] The scientific community rejects ESP due to the absence of an evidence base, the lack of a theory which would explain ESP, and the lack of experimental techniques which can provide reliably positive results; and considers ESP to be pseudoscience.[3][4][5][6][7]

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In the 1930s, at Duke University in North Carolina, J. B. Rhine and his wife Louisa E. Rhine conducted investigation into extrasensory perception. While Louisa Rhine concentrated on collecting accounts of spontaneous cases, J. B. Rhine worked largely in the laboratory, carefully defining terms such as ESP and psi and designing experiments to test them. A simple set of cards was developed, originally called Zener cards[8] – now called ESP cards. They bear the symbols circle, square, wavy lines, cross, and star; there are five cards of each in a pack of 25.

In a telepathy experiment, the "sender" looks at a series of cards while the "receiver" guesses the symbols. To try to observe clairvoyance, the pack of cards is hidden from everyone while the receiver guesses. To try to observe precognition, the order of the cards is determined after the guesses are made. Later he used dice to test for psychokinesis.[9][10]

The parapsychology experiments at Duke evoked criticism from academics and others who challenged the concepts and evidence of ESP. A number of psychological departments attempted to repeat Rhine's experiments with failure. W. S. Cox (1936) from Princeton University with 132 subjects produced 25,064 trials in a playing card ESP experiment. Cox concluded "There is no evidence of extrasensory perception either in the 'average man' or of the group investigated or in any particular individual of that group. The discrepancy between these results and those obtained by Rhine is due either to uncontrollable factors in experimental procedure or to the difference in the subjects."[11] Four other psychological departments failed to replicate Rhine's results.[12]

In 1938, the psychologist Joseph Jastrow wrote that much of the evidence for extrasensory perception collected by Rhine and other parapsychologists was anecdotal, biased, dubious and the result of "faulty observation and familiar human frailties".[13] Rhine's experiments were discredited due to the discovery that sensory leakage or cheating could account for all his results such as the subject being able to read the symbols from the back of the cards and being able to see and hear the experimenter to note subtle clues.[14][15][16][17]

In the 1960s parapsychologists became increasingly interested in the cognitive components of ESP, the subjective experience involved in making ESP responses, and the role of ESP in psychological life. This called for experimental procedures that were not limited to Rhine's favored forced-choice methodology. Such procedures have included dream telepathy experiments, and the ganzfeld experiments (a mild sensory deprivation procedure).[18][19][20]

The scientific consensus does not view extrasensory perception as a real phenomenon.[21][22][23][24][25][26][27] Skeptics have pointed out that there is no viable theory to explain the mechanism behind ESP, and that there are historical cases in which flaws have been discovered in the experimental design of parapsychological studies.[28]

There are many criticisms pertaining to experiments involving Extrasensory Perception, particularly surrounding methodological flaws. These flaws are not unique to a single experimental design, and are effective in discrediting much of the positive research surrounding ESP. Many of the flaws seen in the Zener card experiment are present in the Ganzfeld experiment as well. First is the stacking effect, an error that occurs in ESP research. Trial-by-trial feedback given in studies using a “closed” ESP target sequence (e.g., a deck of cards) violates the condition of independence used for most standard statistical tests. Multiple responses for a single target cannot be evaluated using statistical tests that assume independence of responses. This increases likelihood of card counting and in turn, increases the chances for the subject to guess correctly without using ESP. Another methodological flaw involves cues through sensory leakage. For example, when the subject receives a visual cue. This could be the reflection of a Zener card in the holder’s glasses. In this case, the subject is able to guess the card correctly because they can see it in the reflection, not because of ESP. Finally, poor randomization of target stimuli could be happening. Poor shuffling methods can make the orders of the cards easier to predict, or the cards could’ve been marked and manipulated, again, making it easier to predict which cards come next. [29] The results of a meta-analysis found that when these errors were corrected and accounted for, there was still no significant effect of ESP. Many of the studies only appeared to have significant occurrence of ESP, when in fact, this result was due to the many methodological errors in the research.

^Cordón, Luis A. (2005). Popular psychology: an encyclopedia. Westport, Conn: Greenwood Press. p. 182. ISBN0-313-32457-3. The essential problem is that a large portion of the scientific community, including most research psychologists, regards parapsychology as a pseudoscience, due largely to its failure to move beyond null results in the way science usually does. Ordinarily, when experimental evidence fails repeatedly to support a hypothesis, that hypothesis is abandoned. Within parapsychology, however, more than a century of experimentation has failed even to conclusively demonstrate the mere existence of paranormal phenomenon, yet parapsychologists continue to pursue that elusive goal.

^Joseph Jastrow. (1938). ESP, House of Cards. The American Scholar 8: 13–22.

^Harold Gulliksen. (1938). Extra-Sensory Perception: What Is It?. American Journal of Sociology. Vol. 43, No. 4. pp. 623–634. "Investigating Rhine's methods, we find that his mathematical methods are wrong and that the effect of this error would in some cases be negligible and in others very marked. We find that many of his experiments were set up in a manner which would tend to increase, instead of to diminish, the possibility of systematic clerical errors; and lastly, that the ESP cards can be read from the back."

^Wynn, Charles M; Wiggins, Arthur W. (2001). Quantum Leaps in the Wrong Direction: Where Real Science Ends...and Pseudoscience Begins. Joseph Henry Press. p. 156. ISBN978-0-309-07309-7 "In 1940, Rhine coauthored a book, Extrasensory Perception After Sixty Years in which he suggested that something more than mere guess work was involved in his experiments. He was right! It is now known that the experiments conducted in his laboratory contained serious methodological flaws. Tests often took place with minimal or no screening between the subject and the person administering the test. Subjects could see the backs of cards that were later discovered to be so cheaply printed that a faint outline of the symbol could be seen. Furthermore, in face-to-face tests, subjects could see card faces reflected in the tester’s eyeglasses or cornea. They were even able to (consciously or unconsciously) pick up clues from the tester’s facial expression and voice inflection. In addition, an observant subject could identify the cards by certain irregularities like warped edges, spots on the backs, or design imperfections."

^Hines, Terence. (2003). Pseudoscience and the Paranormal. Prometheus Books. p. 122. ISBN1-57392-979-4 "The procedural errors in the Rhine experiments have been extremely damaging to his claims to have demonstrated the existence of ESP. Equally damaging has been the fact that the results have not replicated when the experiments have been conducted in other laboratories."

^Cogan, Robert. (1998). Critical Thinking: Step by Step. University Press of America. p. 227. ISBN978-0761810674 "When an experiment can't be repeated and get the same result, this tends to show that the result was due to some error in experimental procedure, rather than some real causal process. ESP experiments simply have not turned up any repeatable paranormal phenomena."

^Zechmeister, Eugene B; Johnson, James E. (1992). Critical Thinking: A Functional Approach. Brooks/Cole Pub. Co. p. 115. ISBN0534165966 "There exists no good scientific evidence for the existence of paranormal phenomena such as ESP. To be acceptable to the scientific community, evidence must be both valid and reliable."

^Rothman, Milton A. (1988). A Physicist's Guide to Skepticism. Prometheus Books. p. 193. ISBN978-0-87975-440-2 "Transmission of information through space requires transfer of energy from one place to another. Telepathy requires transmission of an energy-carrying signal directly from one mind to another. All descriptions of ESP imply violations of conservation of energy in one way or another, as well as violations of all the principles of information theory and even of the principle of causality. Strict application of physical principles requires us to say that ESP is impossible."

^Myers, David. (2004). Intuition: Its Powers and Perils. Yale University Press. p. 233. ISBN0-300-09531-7 "After thousands of experiments, no reproducible ESP phenomenon has ever been discovered, nor has any researcher produced any individual who can convincingly demonstrate psychic ability."

^Shermer, Michael. (2003). Psychic drift: Why most scientists do not believe in ESP and psi phenomena. Scientific American 288: 2.

^Stein, Gordon. (1996). The Encyclopedia of the Paranormal. Prometheus Books. p. 249. ISBN1-57392-021-5 "Mainstream science is on the whole very dubious about ESP, and the only way that most scientists will be persuaded is by a demonstration that can be generally reproduced by neutral or even skeptical scientists. This is something that parapsychology has never succeeded in producing."

^Milton, J. & Wiseman, R. (1999). Does psi exist? Lack of replication of an anomalous process of information transfer. Psychological Bulletin, 125, 387–191. - meta-analysis of parapsychological research over 10 years following agreement on methodological criteria by proponents and skeptics.